Power fuses with tubular links and pressure-type link connections



Jan. 8, 1957 F. J. KOZACKA 2,777,033

POWER FUSES WITH TUBULAR LINKS AND PRESSURE-TYPE LINK CONNECTIONS 2Sheets-Sheet 1 Filed June 14, 1954 illlll-IJ Jan. 8, 1957 F. J. KOZACKAPOWER FUSES WITH TUBULAR LINKS AND PRESSURE-TYPE LINK CONNECTIONS 2Sheets-Sheet 2 Filed June 14', 1954 United States Patent POWER FUSESWITH TUBULAR LINKS AND PRESSURE-TYPE LINK CONNECTIONS Frederick J.Kozacka, Ameshury, Mass, assignor to The Chase-Shawmut Company,Newhuryport, Mass.

Application June 14, 1954, Serial No. 436,398

12 Claims. (Cl. 200-420)- This invention relates to the protection ofelectric circuits by means of high-capacity fuses, and more particularlyto improved high-capacity fuse structures for lowvoltage circuits.

High-capacity fuses are preferably current-limiting, i. e. they arepreferably designed to limit the let-through current below the peak ofthe available short-circuit current which the system is capable ofsupplying; Where the current normally carried by the fuse is relativelylarge andwhere it is desired'to achieve a drastic current-limitingaction, the current path through the link must be made up of a pluralityof fusible conductors adapted to be connectedin parallel into theelectric circuit to be protected by' the fuse and these conductors mustbe surrounded by an arc-quenchcing filler, preferably a siliciouspulverul'ent material. Fuses of this type offer a high degreeofshortcircuit protection at relatively moderate cost but are subject toa number of limitations. The magnetic energy inherent in the electricsystem under interruption at the time a majorfault occurs-must in-partbe absorbed by' the arc-quenching filler within the casing; of the fuse.To

this end the fusible conductors within the fuse intended to be connectedin parallel into the electric circuit ought to be arranged in such a waythat each of the conductors issurrounded by a substantially equal amountof" filler; Generally all of the conductors which are connected" inparallel are substantially identical andsupposed to fuse simultaneouslyby'the heat generated by any major fault current. Manufacturingtolerances are of no consequence only as long as these tolerances areextremely small. Relatively small and absolutely unavoidabledifferences. between theparallel' fusible conductors have a tendency toresult in improper operation of the fuse. Considering a pair ofparallelconductors of which one fuses before the other, a small breakwill form at the. first fused conductor'by reason of the fusion thereof;however, sincethe first fused conductor is shunted by the second"conductor the voltage across the small fusion break. will be close to,zero andmay beinsufiicient'to kindle an arc across the fusion gap and tocause gap growth on account of-backburning by the arc.. When theotherconductor fuses an arc gap will form and that arcgap will grow by virtueof back-burning. However, the small break formed in. the firstfused'conductor will not grow and the arc-quenching filler surroundingthat conductor willnotbe utilized in. the interrupting process, i. e.for absorbing. a portion of the magnetic energy inherentin the electricsystem at the time of the occurrence of the fault. In other words, thearc-quenching filler surrounding the first fused conductor. is not beingused at all in the process of circuit. interruption. I

In a fuse having many conductors in parallel, a substan tial portion ofthe arc-quenching filler withinthe casing may remain unused, orinoperative as an energy absorber. during interruption ofja faulted.circuit by the fuse. Because of'this phenomenon, the interruptingefiieiencyof, the arc-quenching filiermay be small. As a' result,highcapacity' current-limiting fuses comprising a plurality of PatentedJan. 8, i957 fusible conductors in parallel are generally provided withlarger numbers of fusible conductors, larger quantities of arc-quenchingfiller and casings of larger size than actually necessary if eachelement of the fuse assumed an approximately equal share in the totalinterrupting duty of the fuse upon occurrence of a major fault.

Providing a plurality of fusible conductors in a fuse intended to beconnected in parallel into the circuit to be protected by the fuseresults also in the relatively difiicult problem of conductivelyconnecting the ends of the conductors to theterminals of the fuse.Spot-welding is one possible answer to the problem but spot-Welds have atendency to come off if not carefully made by highly skilled labor. Spotwelds are particularly difficult to achieve if the mass of the terminalsof the fuse is large, as is widely adopted" practice in this country.Soldering with soft solder is another possibility of securing fuse linksto terminal elements. Since terminal elements of high capacity fusesinvolve frequently a very large mass, it may be difficul't to heat themass up to the temperature required for soldering.

Another drawback of high-capacity multiple fusible conductor fuseshaving ribbon type fusible conductors adapted to be connected inparallel into the electric circuit which the fuse is to protect residesin the fact that an additional spacer is genera-11y required to maintainthe terminal elements in the proper spaced relation if the terminalelements involve a substantial mass, as is frequently the case, asmentioned before.

It is the primary object ofthis invention. to provide high-capacityfuses which are entirely free from all the above referred-to drawbacksand/ or limitations.

Another object of this invention is to provide currentlimiting fuseswhich are less expensive to manufacture and which have. a higherinterrupting efiiciency than comparable prior art high-capacity fuses.

Still another object of this invention is to provide current-limitingfuses having tubular fuse links yet not' being subject to thelimitations and/ or drawbacks of prior,

art fuses having fuse links of this type.

A further object of this invention is to provide highcapacity fuses thelinks of which can readily be removed and replaced upon blowing of thefuses.

A further object of this invention is to modify and improve thestructure disclosed and claimed in my United StatesfPa'tent 2,665,348,January. 5, 1954, Current-Limiting Fuse, assigned to the same assigneeas the present invention.

The foregoing and other general and special objects of the invention andadvantages thereof will more clearly appear from the ensuing particulardescription of the invention, as illustrated in'the accompanyingdrawings wherein:

Fig. 1 is a perspective view of a portion of a fuse embodying myinvention;

Fig. 2 is. a front view of a fuse link of sheet metal for a fuseembodying my invention;

,Fig. 3 is a longitudinal section along 3-3 of Fig. 4 showing, a fuseembodying my invention;

Fig. 4 is a cross-section. taken along 4-4 of Fig. 3;

Fig- 5 is a longitudinal section along 55 of Fig; 6 showing: anotherembodiment of the invention;

Fig. 6' is. a cross-section taken along 6-6 of Fig. 5;

Fig. 7 is. a. longitudinal section of a third embodiment of. myinvention taken along 7-7 of Fig. 8, and

Fig. 8 is a cross-section of the structureshown in Fig. 7 taken, along8-8 of Fig. 7.

Referringnow to the drawings, and more particularly to Figs. 1: to 4,inclusive, reference numeral 1 has been applied; to indicate. a tubularfuse link. Fuse link 1 is formed by Winding the stamping shownin'Fig; 2into the" shape ofa cylinder, as clearly shown in Figs. 1, 3 and 4.

Fuse link 1 extends between a pair of spaced massive terminal elements 2of copper, of which each comprises a substantially cylindrical block ofcopper. Each ter minal element 2 is provided with a blade contact 3inserted into a groove 2a in the respective terminal element. Casing 4of insulating material is slipped over terminal elements 2 and pinned tothe latter by means of steel pins 5.

Casing 4 may either consist of a ceramic substance, or of aglass-cloth-laminate including a plastic fairly heat resisting material.Each terminal element 2 is provided with a shoulder s, subdividing theterminal element into a portion 212 of relatively small diameter andinto a portion 20 of relatively large diameter. The portion ofrelatively large diameter 20 supports casing 4. The portion ofrelatively small diameter 2b of each terminal element 2 forms acylindrical clamping surface for securing link 1 to, and conductivelyconnecting link 1 with, the respective terminal element 2. To this end asplit clamping ring 6 is mounted on each of the axially outer ends oflink 1 and split rings 6 engage under pressure link 1 and press link 1against the clamping surfaces 2b of the terminal elements 2. The outernon-split or continuous rings 7 are mounted under pressure upon theinner or split rings 6, and establish a firm mechanical connectionbetween link 1 and terminal elements 2 having a very small electricinterface resistance.

Ribbon type fuse link 1 is wound cylindrically to fit upon thecylindrical clamping surface 2b on each terminal element 2 and arrangedwithin casing 4 in coaxial rela tion thereto. Link 1 is provided with aplurality of groups G1, G2, G3 of perforations 1a and intermediatecurrent-carrying elements 1b. Each of said groups G1, G2, G3 comprises aplurality of narrowly spaced perforations 1a having a predeterminedwidth and a plurality of intermediate current-carrying elements 1barranged in circular relation in a plane at right angles to the axis ofthe cylindrical surface defined by link 1.

Upon occurrence of a fault current of major proportions, all theintermediate current-carrying elements 1b fuse substantiallysimultaneously. Each group of perforations G1, G2, G3 comprises 10square perforations 1a and 10 intermediate current carrying elements 1b,and therefore the link behaves basically in the same fashion 1bimmediately adjacent thereto. The stippled area in electric circuit, andof which each has three serially related necks, or points of reducedcross-sectional area. As in any fuse having a plurality of fuse linksconnected in parallel, some of the necks, or portions of reducedcross-sectional area, or current-carrying elements 1b, will fuserelatively soon and others relatively late. The first fused elements 1bform mere fusion gaps across of which there is virtually no voltage atthe time of gap formation. Hence no arc is kindled and no back-burningtakes place at these gaps. A voltage will prevail across the last formedgaps and cause kindling of arclets at these gaps, which arclets willburn back, resulting in progressive growth of the arc gaps andprogressive increase of the arc voltage.

Referring now to Fig. 2, and more particularly to the twocurrent-carrying elements 1!) at the left end of group G1; assuming thatthe element 1b way to the left fuses after the element in group G1 whichis second from the left edge of link 1. An extremely narrow gap may beformed in the first fused element 117, which gap may be alreadyrelatively cool at the time the element 1b which fuses last fuses, andgives rise to the formation of an arclet. The Width W1 of theperforations 1a is sufficiently small to cause vaporization of theelement 112 second from the left edge of link 1, i. e. of the firstfused element 1b, by back-burning of the arclet formed at the element115 way to the left of group G1, i. e. the element 1b to fuse last. Thussubstantially the entire pulverulent arcquenching filler surrounding thelink will be used as an energy absorber, irrespective of whether or notan are gap is initially formed at all points of break, or at allcurrent-carrying elements 111. In other words, the width M of theperforations 1a is sufiiciently small to cause vaporization of any ofthe plurality of current-carrying elements 1b by back-burning of the areformed at a major fault at one of said plurality of current-carryingelements 112 immediately adjacent thereto. The stippled area in Fig. 2is indicative of the amount of back-burning oc curring when a merefusion break without arcing is formed at the current-carrying element112 second from the left in group G1, and an arc is kindled upon fusionof the current-carrying element 1b way to the left of group G1.

The number of perforations la in each group G1, G2, G3, their width W1,and the dimensions of the currentcarrying elements 1b depend upon anumber of factors. These parameters must be determined separately foreach design. The number of perforations 1a required in each case mayreadily be determined experimentally from the above back-burningcondition. As a general rule, the number of perforations in each groupG1, G2, G3 should be larger than five. The number of groups G1, G2, G3depends upon the arc voltage which it is desired to obtain and upon thedesired rate of rise of the arc voltage. Where the circuit voltage islow and the current-limiting action which it is desired to achieve notvery high, one single group of perforations la and intermediatecurrentcarrying elements 1b may be sufficient. Generally several groupsG1, G2, G3 etc. of perforations 1a and intermediate current-carryingelements 1b should be provided, provision of each additional groupincreasing by one the number of serially related arclets forming duringthe process of interruption. As clearly shown in Fig. 2, eachperforation 1a is rectangular and has a pair of relatively narrow sidesand a pair of relatively wide sides. The narrow sides of perforations 1aextend parallel to the axis of the cylindrical surface defined by link1, as can best be seen in Figs. 1 and 3. Reference character W2indicates the Width of the current-carrying elements 1b. The length w ofthe wide sides is a multiple of the length W3 of the narrow sides. Theratio of the sum total of the lengths w of said wide series to the sumtotal of the widths wz of current-carrying elements 1b should be smallerthan 10:1. This enables to achieve a considerable bending strengthwithout sacrificing arc voltage. A number of serially related groups G1,G2, G3, etc. of perforations la and current-carrying elements 1b enablesto build-up arc voltage to exactly the amount required. The ratio ofws/wl should preferably be in the order of Winding of a link of sheetmetal in the shape of a cylinder greatly increases the mechanicalstrength, and more particularly the bending strength, of the link. It isthus possible to impart sufficient mechanical strength to the link toenable the link when clamped to the clamping surfaces 2b of the pair ofterminal elements 2 to form jointly with the pair of terminal elements 2a selfsustained structural unit, i. e. a unit which does not require aspacer, or mechanical tie, in addition to link 1, for maintaining theterminal elements 2 in the proper spaced relation thereof. Themechanical strength of tubular link 1 is not seriously impaired by thegroups G1, G2, G3 of perforations 1a, i. e. link 1 does not lose itsability because of perforations 1a to tie the two terminal elements 2mechanically into a structural unit that does not require an additionalinsulating spacer. The relatively shortlength W3 of current-carryingelements 112 is mainly responsible for the ability of link 1 to operateas a spacer for the heavy masses 2, 3 attached to the ends thereof.While theshort length W3 of current-carrying elements 1b increases thebending strength of the terminal-elementlink-unit 1, 2, the shortness oftheir length W3 imposes a limitation with regard to the magnitude of thearc voltage which can be produced at each single point of reducedcross-sectional area, or at each break. As mentioned above, the arcvoltage required in any particular instance can be readily produced byproviding several serially related groups G1, G2, G3 of perforations 1aand currentcarrying elements 1b of reduced cross-sectional area.

As mentioned before, the axially outer ends of link 1 are eachsurrounded by a split ring 6, and an outer nonsplit or continuous ring 7is mounted under pressure upon each split ring 6. The radial pressure ofrings 7 upon rings 6 ought to be considerable to compress split rings 6,as required to minimize the voltage drop between link 1 and clampingsurfaces 2b, thus minimizing heat losses occurring within the fuse. Thisconsiderable amount of pressure should preferably be achieved withoutresorting to heating, or cooling, of any part of the structure. In theembodiment of the invention shown in Figs. 3 and 4 the requisitepressure is being achieved by chamfering slightly the axially outer endsof rings 7. The degree of chamfering is so slight that this feature doesnot appear in the drawing. The difference between the outer diameter ofsplit rings 6 in the compressed position thereof and the inner diameterof continuous rings 7 should be as small as possible.

In the process of manufacturing the fuse a subassembly is first producedcomprising link 1', terminal elements 2, including blade contacts 3, andrings 6 and 7, all joined together to form a self-sustained structuralunit. This unit is then shoved into casing 4 in such a way as to leave asmall gap between casing 4' and one of the copper blocks of terminalelements 2. This small gap is used as filling gap for introducing thearc-quenching filler, or quartz sand 8, into the casing 4. The two edges1 of link 1' define a gap 1d extending in a direction longitudinally ofthe link. When the fuse is being filled with quartz sand, or anequivalent pulverulent filler, the. sand penetrates through gap 1d intothe space inside of link 1. Thus link 1 is ultimately surrounded both onthe outside and on the inside thereof by the arc-extinguishing filler 8.When the space within casing 1 is completely filled with sand, thecasing 4 is shoved into the position shown in Fig. 3 and the fuse issubjected to vibrations which cause the filler 8 within casing 4 tosettle, resulting in a more dense packing of link 1 in the filler 8.Thereupon casing 4 is re-opened, some filler added, and pins 5 areinserted to preclude the casing 4 from coming off the terminal elements2. If desired, several vibrating and re-filling operations may beincluded in the manufacturing process of the fuse.

The fuse link structure shown in Figs. 1, 3 and 4 is adapted to rapidlyinterrupt major fault currents. Where it is desirable to interruptprotracted overload currents, in addition to major fault currents, asmall rivet 12 of tin, tin-indium alloy, or other suitable low fusingpoint metal is arranged immediately adjacent one end ofeachcurrentcarrying element. As clearly shown in Fig. 1, two lines ofrivets made of a low fusing point metal are arranged on opposite ends ofcurrent-carrying elements 111 each out of registry with the other. Onoccurrence of overloads of inadmissible duration rivets 12 melt, and themetal of which they are made forms an alloy with the metal of which thelink proper is made. The link proper is made of a metal which has arelatively high fusing point and a relatively small heat-currentintegral, preferably silver. The alloys of silver and tin, or silver andindium, have a relatively high resistance, resulting in increased i -rlosses at the points where rivets 12 are located. As a result, heatgeneration is stepped up at these points, and this is conducive to therapid formation of interrupting breaks. Upon fusion of rivets 12 thefused low-melting point metal tends to fiow toward the current-carryingelements 1b and these are, therefore, the points where alloy-formation,increase of resistance, and formation of circuit interrupting gaps tendto take place. Interruption of all the current-carrying elements 1b inthe group G2 forms a circular break, or; gap-,.which precludes continuedflow of current.

Rivets 12 do not significantlythrough the fuse structure.

6 affect the mechanicalstrength oflink. 1 and do not deprive it of itscharacter as a unitary sheet metal structure.

The fuselinkshown in Figs. 5 to 8, inclusive, is identical with the fuselink shown in Figs. 1 to- 4, inclusive, and therefore does not need tobe described again hereinafter.

According to Figs. 5 and 6 the terminal copper blocks have a portion 20the diameter of which is relatively large and a portion 217 the diameterof which is relatively small. Portion 2c supports the tubular insulatingcasing d and portion 2b supports the tubular fuse link 1. A pair ofclamping rings 9 comprising the tightening screws 10 firmly clamp theaxially outer ends of link 1 against the portions 2b of the terminalblocks. Pins 5 of steel provide a solid mechanical connection betwen thetermiblocks and casing4.

Referring now to Figs; 7 and 8, each of the two cylindri'cal terminalblocks is provided with a coaxial groove A pair of slotted rings Il aand 11b is accommodated in each groove 2g. The radially inner rings 11bare in physical engagement with the surface of tubular link 1 and theradially outer rings are mounted upon the radially inner rings 11b. Theradially outer rings 11a are wedge shaped and compress the radiallyinner rings 11b when driven into the grooves 2g, thus causing rings 11bto exert considerable pressure upon link 1 and terminal. blocks andminimizing interface resistance between link i and copper blocks 2. Theslot in rings 11a, 116 as well as the slots of rings 6 in Fig. 1 greatlyincreases the flexibility thereof.

It will be understood that I have illustrated and de scribed hereinpreferred embodiments only of the invention and that various alterationsmay be made in thedetails thereof without departing from the spirit" andscope of the invention as defined in the appended claims.

I claim as my invention:

1. A high-capacity fuse comprising a casing of insulating material, apair of terminal elements one at each end of said casing, each of saidpair of terminal elements having a cylindrical surface of relativelylarge diameter supporting said casing and a coaxial cylindrical clampingsurface of relatively small diameter on the side thereof adjacent theinside of said casing, a ribbon-type fuse link of silver cylindricallywound to fit upon said cylindrical clamping surface on each of said pairof terminal elements arranged within said casing and maintained incoaxial relation thereto by engagement' with said clamping surface oneach of said pair of terminal elements, said link being provided with aplurality of groups of perforations and intermediate current-carryingelements, each of said groups comprising a plurality of narrowly spacedperforations having a predetermined length substantially less than theoverall length of said link and a predeter mined width and a pluralityof intermediate currentcarrying elements arranged in circular relationin a plane at right angles to the axis of the cylindrical surfacedefined by said link, said predetermined width of each of said pluralityof perforations being sufiiciently small to cause vaporization of any ofsaid plurality of currentcarrying elements by back-burning of the arcformed at a major fault at one of said plurality of current-carryingelements immediately adjacent thereto, said link consisting of a unitarysheet of metal having sufiicient mechanical strength to form jointlywith said pair of terminal elements a self-sustained structural unitwhen clamped to said clamping surface of each of said pair of terminalelements, a pair of clamping rings clamping each end of said link tosaid clamping surface of one of said pair of terminal elements and apulverulent silicious filler in the space between said casing and saidlink and in the space inside of said link.

2. A high-capacity fuse comprising a casing of insulat ing material, asilicious arc-quenching filler within said casing, a pair of terminalelements one on each end ofv said casing, each of said'pair of terminalelements having a cylindrical clamping surface on the side thereofadjacent the center of said casing, a ribbon-type fuse link of silverwound cylindrically to fit upon said cylindrical clamping surface oneach of said pair of terminal elements arranged within said casing andmaintained in coaxial relation thereto by engagement with said clampingsurface on each of said pair of terminal elements, said link beingprovided with a group of narrowly spaced perforations having apredetermined length substantially less than the overall length of saidlink and a predetermined width and a plurality of intermediatecurrent-carrying elements arranged in circular relation in a plane atright angles to the axis of the cylindrical surface defined by saidlink, said predetermined width of each of said plurality of perforationsbeing sufficiently small to cause vaporization of any of said pluralityof current-carrying elements by back-burning of the are formed at amajor fault at one of said plurality of current-carrying elementsimmediately adjacent thereto, said link having sufiicient mechanicalstrength to form a self-sustained structural unit jointly with said pairof terminal elements when clamped to said clamping surface of each ofsaid pair of terminal elements, a pair of clamping rings clamping eachend of said link to said clamping surface of one of said pair ofterminal elements, and a filler of quartz sand in the space between saidcasing and said link and in the space inside said link.

3. A high-capacity fuse comprising a casing of insulating material, apulverulent filler within said casing, a pair of terminal elements oneat each end of said casing, each of said pair of terminal elementshaving'a cylindrical surface of relatively large diameter supportingsaid casing and a coaxial cylindrical clamping surface of relativelysmall diameter on the side thereof adjacent the inside of said casing, aribbon-type fuse link of silver wound cylindrically to fit upon saidcylindrical clamping surface on each of said pair of terminal elementsarranged Within said casing and maintained in coaxial relation theretoby engagement with said clamping surface on each of said pair ofterminal elements, said link being provided with a plurality of groupsof perforations and intermediate currentcarrying elements, each of saidgroups comprising more than five narrowly spaced rectangularperforations and intermediate current-carrying elements arranged incircular relation in a plane at right angles to the axis of thecylindrical surface defined by said link, each of said perforationshaving a pair of relatively narrow sides and a pair of relatively widesides, said narrow sides of each of said perforations extending parallelto the axis of the cylindrical surface defined by said link and thelength of said Wide sides of each of said perforations being a multipleof the length of said narrow sides thereof, a pair of clamping ringsclamping each end of said link to said clamping surface of one of saidpair of terminal elements, a body of quartz sand in engagement with theradially inner surface of said link and a body of quartz sand inengagement with the radially outer surface of said link.

4. A high-capacity fuse comprising a casing of insulating material, apulverulent arc-quenching filler Within said casing, a pair of terminalelements one at each end of said casing, each of said pair of terminalelements having a cylindrical surface of relatively large diametersupporting said casing and a coaxial cylindrical clamping surface ofrelatively small diameter on the sidc thcreof adjacent the inside ofsaid casing, a ribbon-type fuse link wound cylindrically to fit uponsaid cylindrical clamping surface on each of said pair of terminalelements arranged within said casing and maintained in coaxial relationthereto by engagement with said clamping surface on each of said pair ofterminal elements, said link being provided with a plurality of groupsof perforations and intermediate current-carrying elements, each of saidgroup comprising a plurality of narrowly spaced perforations having apredetermined Width and a plurality of intermediate currentcarryingelements arranged in circular relation in a plane at right angles to theaxis of the cylindrical surface defined by said link, said predeterminedwidth of each of said plurality of perforations being sufiiciently smallto cause vaporization of any of said plurality of current-carryingelements by back-burning of the are formed at a major fault at one ofsaid plurality of current-carrying elements immediately adjacentthereto, said link consisting of a unitary sheet metal having asufficient mechanical strength to form jointly with said pair ofterminal elements a selfsustained structural unit when clamped to saidclamping surface of each of said pair of terminal elements, and an nularclamping means for clamping each end of said link to said clampingsurface of each said pair of terminal elements, said annular clampingmeans comprising a pair of rings arranged on each end of said link, atleast one of said pair of rings being radially split for increasedflexibility.

5. A high-capacity fuse comprising a casing of insulating material, apulvemlent arc-quenching filler within said casing, a pair of terminalelements one at each end of said casing, each of said pair of terminalelements having a cylindrical clamping surface on the side thereofadjacent the inside of said casing, the diameter of each said clampingsurface being smaller than the diameter of said casing and each saidclamping surface being situated within said casing, a ribbon-type fuselink cylindrically wound to fit upon said cylindrical clamping surfaceon each of said pair of terminal elements arranged Within said casingand maintained in coaxial relation thereto by engagement with saidclamping surface on each of said pair of terminal elements, said linkbeing provided with a plurality of groups of perforations andintermediate current-carrying elements, each of said groups comprisingmore than five narrowly spaced rectangular perforations and intermediatecurrent-carrying elements arranged in circular relation in a plane atright angles to the axis of the cylindrical surface defined by saidlink, each of said perforations having a pair of relatively narrow sidesand a pair of relatively wide sides, said narrow sides of each of saidperforations extending parallel to the axis of the cylindrical surfacedefined by said link and the length of said wide sides of each of saidperforations being a multiple-of the length of said narrow sidesthereof, the ratio of the sum total of the lengths of said wide sides tothe sum total of the width of said intermediate current-carryingelements being smaller than 10:1, said link consisting of a sheet metalhaving sufficient mechanical strength to form a self-sustainedstructural unit jointly with said pair of terminal elements when clampedto said clamping surface of each said pair of terminal elements, andannular clamping means for clamping each end of said link to saidclamping surface of each of said pair of terminal elements, said annularclamping means comprising a pair of rings arranged on each end of saidlink, at least one of said pair of rings being radially split forincreased flexibility.

6. A high-capacity fuse comprising a casing of insulating material, apair of terminal elements one at each end of said casing, each of saidpair of terminal elements having a cylindrical clamping surface on theside thereof adjacent .the inside of said casing, the diameter of eachsaid clam-ping surface being smaller than the diameter of said casingand, each said clamping surface being situated within said casing, arib'bontype fuse link cylindrioally wound to fit upon said cylindricalclamping surface on each of said pair of terminal elements arrangedWithin said casing and maintained in co'axia l relation thereto 'by saidclamping surface on each of said pair of terminal elements, said linkhaving a plurality of groups of perforations and intermediatecurrent-carrying elements, each of said groups comprising a plurality ofnarrowly spaced perforations having a predetermined width and aplurality of intermediate current-carrying elements arranged in circularrelation in a plane at right angles to the axis of the cylindricalsurface defined by said link, said predetermined width of each of saidplurality of perforations being sufficiently small to cause vaporizationof any of said plurality of current-carrying elements by, back-burningofthe are formed at a major fault at one of said plurality ofcurrent-carrying elements immediately adjacent thereto, said linkconsisting of one single stamped, out piece of sheet metal providingsulficient mechanical strength to cause said link to form a structuralunit jointly with said pair of terminal elements when clamped to saidclamping surface of each said pair of terminal elements, a plurality ofrivets of a low melting point metal arranged in said link immediatelyadjacent =to one of said plurality of current ca-rrying elements, and apair of clamping rings clamping each end of said link to said clampingsurface on one of said pair .of terminal elements.

7. A high-capacity fuse comprising a casing of insulating material, apulverulent arc-quenching filler within said casing, a pair of terminalelements one at each end of said casing, each of said pair of terminalelements comprising a copper block being substantially cylindrical andhaving a portion of relatively large diameter at the end thereof remotefrom the center of said casing and a portion of relatively smalldiameter at the end thereof adjacent to the center of said casing, saidportion of relatively large diameter of said copper block of each ofsaid pair of terminal elements fitting into and supporting said casing,a fuse link of sheet metal bent substantially in the shape of a cylinderengaged at the inside thereof by said portion of relatively smalldiameter of said copper block of each of said pair of terminal elements,a pair of split rings one at each end of said link, and a pair ofcontinuous rings each mounted upon one of said pair of split rings topress said one of said pair of split rings against one of the ends ofsaid link and against said portion of relatively small diameter of saidcopper block of each of said pair of terminal elements.

8. A high-capacity fuse comprising :a casing of insulating material, apair of terminal elements one at each end of said casing, each of saidpair of terminal elements comprising a substantially cylindrical blockof metal having a portion of relatively large diameter at the endthereof remote from the center of said casing and a portion ofrelatively small diameter at the end thereof adjacent the center of saidcasing, said portion of relatively large diameter fitting into andsupporting said casing, a fuse link of sheet metal bent substantially inthe shape of a cylinder engaged at the inside thereof by said portion ofrelatively small diameter of said block of metal of each of said pair ofterminal elements, said link being provided with a plurality of groupsof perforations each arranged in circular relation in a separate planeat right angles to the axis of the cylindrical surface defined by saidlink, said link having suflicient mechanical strength to form jointlywith said pair of terminal elements a self-sustained structural unitwhen clamped to said portion of relatively small diameter of said blockof metal of each of said pair of terminal elements, and a pair ofannular clamping means for clamping the portions of said link engaged bysaid portions of relatively small diameter of said block of metal ofeach of said pair of terminal elements to said portion of relativelysmall diameter of said block of metal of each of said pair of terminalelements.

9. A high-capacity fuse comprising a casing of insul-ating material, .apulverulent arc-quenching filler within said casing, a pair of terminalelements one at each end of said casing, each of said pair of terminalelements having a portion of relatively large diameter at the endthereof remote from the center of said casing and a portion ofrelatively small diameter at the end thereof adjacent the center of saidcasing, said portion of relat-ively large diameter fitting into andsupporting said casing, a fuse link of sheet metal bent substantially inthe shape of a cylinder fitted upon and supported by said portion ofrelatively small diameter of each of said pair of terminal elements,said link being provided with a plurality of groups of perforations eacharranged in circular relation, in a separate plane at right angles tothe axis of the cylindrical surface defined by said link, said linkhaving sufiicient mechanical strength to form jointly with said pair of.terminal elements. a self-sustained structural unit when clamped to saidportion of relatively small di ameter of each, of said pair of terminalelements, a pair of split rings one at each end of said link, and a pairof continuous rings each mounted under pressure upon one of said pair ofsplit rings to press said one of said pair of split rings against one ofthe ends of said link and against said portion of relatively smalldiameter of each of said pair of terminal elements.

1.0. A. high-capacity fuse comprising a casing of insu-v latingmaterial, a pulverulent arc-quenching filler within said casing, a pairof terminal elements one at each end of said casing, each of said pairof terminal elements having a portion of relatively large diameter atthe end thereof remote from the center of said casing and a portion ofrelatively small diameter at the end thereof adjacent the center of saidcasing, said portion of relatively large diameter fitting into andsupporting said casing, a fuse link of sheet metal bent substantially inthe shape of a cylinder fitted upon and supported by said portion ofrelatively small diameter of each of said pair of terminal elements,said link being provided with a plurality of groups of perforations andintermediate current-carrying elements, each of said group comprising aplurality of narrowly spaced perforations having a predetermined widthand a plurality of intermediate current-carrying elements arranged incircular relation in a plane at right angles to the axis of thecylindrical surface defined by said link, said predetermined width ofeach of said plurality of perforations being sufiiciently small to causevaporization of any of said plurality of current-carrying elements byback-burning of the are formed at a major fault at one said plurality ofcurrent-carrying elements immediately adjacent thereto, said link havingsufficient mechanical strength to form jointly with said pair ofterminal elements a self-sustained structural unit when clamped to saidportion of relatively small diameter of each of said pair of terminalelements, a pair of split rings one at each end of said link, and a pairof continuous rings each mounted under pressure upon one of said pair ofsplit rings to press said one of said pair of split rings against one ofthe ends of said link and against said portion of relatively smalldiameter of each of said pair of terminal elements.

1'1. A high-capacity fuse comprising a casing of insulating material, apair of metal blocks circular in crosssection having the same diameteras the inside diameter of said casing each fitted into one of the endsof said casing, a pair of blade contacts each projecting trom one ofsaid pair of metal blocks in a direction away from said casing, a pairof cylindrical link-supports circular in cross-section having a smallerdiameter than said inside diameter of said casing, each of said pair oflink-supports forming an integral coaxial part of one of said pair ofmetal blocks projecting therefrom toward and into said casing, aribbon-type fuse link substantially in the shape of a cylinder havingthe same inside diameter as the diameter of said pair of link-supportsmounted on and held by said pair of link-supports in coaxial relationwith respect .to said casing, said link consisting of a stamping ofsheet silver adapted to provide a continuous current path from one ofsaid pair of link-supports to the other of said pair of link-supports,clamping ring means for clamping said link to said pair oflink-supports, a first body of quartz sand inside said fuse link and asecond body of quartz sand in the space between said fuse link and saidcasing.

:12. A high-capacity fuse comprising a casing of insulating material, apair of metal block-s circular in crosssection having the same diameteras the inside of said casing each fitted into one of the ends of saidcasing, a pair of blade contacts each projecting from one of said pairof metal blocks in a direction away from said casing, a pair ofcylindricallink-supports circular in crosssection having a smallerdiameter than the inside diameter of said casing, each of said pair oflink-supports forming an integral coaxial part of one of said pair ofmetal blocks projecting therefrom toward and into said casing, aribbon-type fuse link substantially in the shape of a cylinder havingthe same inside diameter as the diameter of said pair of link-supportsmounted on and held 'by said pair of link-supports in coaxial relationwith respect to said casing, said link consisting essentially of astamping of high conductivity high fusing point sheet metal adapted toprovide a continuous current path within said metal from one of saidpair of link-supports to the other of said pair of link-supports, saidstamping having a plurality of stamped-out portions providing aplurality of points of reduced cross-sectional area, said link furtherhaving sufiicicnt bending-strength in spite of said plurality of pointsof reduced cross-sectional area to form jointly with said pair of metalblocks a self-sustained structural unit when clamped to said pair oflink-supports, and clamping ring means for clamping said link to saidpair of link supports.

References Cited in the file of this patent UNITED STATES PATENTS1,207,351 Wake Dec. 5, 1916 1,215,999 Schweitzer Feb. 13, 1917 1,716,884Goss June 11, 1929 1,828,277 Bennett Oct. 20, 1931 2,287,553 'FlotenJune 23, 1942 2,625,626 Matthysse Jan. 13, 1953 FOREIGN PATENTS 20,483Great Britain Sept. 19, 1902

